Interesting idea. There are some products along these lines. I have a series of maps that I sell directly through RPGNow. These are just a single map, sliced up into printable chunks and bundled into a pdf, along with the high res gridded and ungridded jpg for use in tabletop play. These get sold through all the one bookshelf stores including ENWorld and Paizo. They sell for $1 at the moment, but I think that's a little low. I'd say $2 is fine for a single, usable map. The reviews back this up. I'd say that 3 maps with associated text for $15 seems like a good price on those numbers. I'll be interested to see how that goes.
Make sure that you provide a printer friendly greyscale version of your chopped up map. There's nothing worse than buying a $15 pdf and then finding out you need to replace your printer cartridge twice just to print the pages.
Sounds like a great venture. I look forward to hearing how it goes.